Antibodies are a type of protein that the immune system uses to recognize and neutralize foreign objects such as bacteria, viruses, and other harmful substances. The portion of the antibody that binds to the foreign substance is called a "ligand," and the substance itself is often referred to as an "antigen."

Monoclonal antibodies are antibodies that are made by identical immune cells that are all clones of a unique parent cell. They have monovalent affinity, in that they bind to the same epitope (the part of an antigen that is recognized by the antibody).

Therapeutic monoclonal antibodies are engineered to serve various therapeutic purposes. These include:

1. Cancer Treatment: Monoclonal antibodies can be designed to attach to specific proteins on cancer cells, marking them for destruction by the immune system. Examples include trastuzumab (Herceptin?) for HER2-positive breast cancer and rituximab (Rituxan?) for certain types of lymphoma.

2. Autoimmune Disorders: Some monoclonal antibodies are designed to target and neutralize specific immune system components that are overactive in autoimmune diseases. For example, adalimumab (Humira?) and infliximab (Remicade?) are used for conditions like rheumatoid arthritis and Crohn's disease.

3. Infectious Diseases: Monoclonal antibodies can be used to neutralize infectious pathogens. This has been especially prominent in the response to the COVID-19 pandemic, with the development of monoclonal antibodies like bamlanivimab and etesevimab.

4. Other Conditions: There are also monoclonal antibodies for conditions like asthma (omalizumab/Xolair?), high cholesterol (evolocumab/Repatha? and alirocumab/Praluent?), and osteoporosis (denosumab/Prolia?).

In general, the primary advantage of monoclonal antibodies is their specificity. They can be engineered to bind very precisely to their target, minimizing off-target effects and potentially improving the safety and effectiveness of treatment. As of my knowledge cutoff in September 2021, monoclonal antibodies remain a very active area of research and development, with many new therapies in preclinical and clinical trials.